Written by

Marc Saltzman
Special for USA TODAY

Considering that Plants vs. Zombies 2 has been downloaded more than 20 million times from the App Store so far, chances are you're one of the many enjoying the time-traveling sequel.

Initially available exclusively for iPhone, iPad and iPod touch (free-to-play but with in-app purchases), EA Mobile's zany "tower defense" strategy game can get quite challenging. USA TODAY caught up with lead designer Mohan Rajagopolan and senior producer Bernie Yee to share some handy tips - 20 of them, in fact - to mastering the game.

As the name suggests, Plants vs. Zombies 2 pits garden vegetation against ...